The ultrastructure of the gap junction intercellular channel will be further elucidated using diffusion analysis under varied conditions such as solvent exchange and alteration of cell water viscosity. Elemental analysis and standard E M will be used to study ion content and cell structure respectively. Fickian diffusion analysis is applied to cells linked by gap junctions. The cells are cylindrical in shape and the junctions occur at the ends of the cells. Both cytoplasmic diffusion coefficient and junctional membrane permeability can be determined. The analysis has potential in determining the parameters which affect solute diffusion in both the cytosol and the intercellular channel. The analysis should elucidate the role of solute-solute interaction in determining a solute's transit time through a gap junction and will define the physical chemical processes which affect a solute's mobility in the cytoplasm of a cell.